Inhibition of corrosive action of fluid deicer composition

ABSTRACT

Cadmium, aluminum and magnesium metal corrosion by an aqueous deicer solution containing urea, ammonium nitrate and ethylene glycol is inhibited by incorporating therein about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt and about 0.05 percent to 0.40 percent by weight of a water-soluble chromate salt. The deicer solution is preferably for use to deice aircraft runways.

United States Patent 1 1 I 1 I 1 I 1 Inventors Herbert F. Scott, Jr.

Prince George; William P. Moore, Chester, both 01 Va. Appl Nu 15,292 i'llmi V01). 27. I970 Patented Nov. 30, 197i Assignee Allied Chemical Corporation New York, N.Y.

by said Scott and said Moore INHIBITION OF CORROSIVE ACTION OF FLUID DEICER COMPOSITION 10 Claims, No Drawings 11.8. C1 252/70, 106/13, 252/389, 252/391 Int. Cl C09k 3/18, C23f11/l4,C23fl1/18 Field of Search 252/70,

[56] References Cited UNITED STATES PATENTS 2,582,129 1/1952 Jacoby 2,692,860 10/1954 Barker... 3,108,075 10/1963 Hearst 3,185,648 5/1965 Standish et a1. 3,240,708 3/1966 Dulat et al. 3,297,577 1/1967 Standish et a1 Primary Egamirrer- Leon D. Rosdol Assistant Examiner-Harris A. Pitlick Attorneys-John J. Lipari and Fred L. Kelly runways.

INHIBITION OF CORROSIVE ACTION OF FLUID DEICER COMPOSITION CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to U.S. Pat. application No. 824,808, filed May 15, 1969, for Deicer Composition.

BACKGROUND OF THE INVENTION This invention relates to a chemical deicer composition containing urea, ammonium nitrate and ethylene glycol; in particular, it relates to the inhibition of the corrosive action thereof on cadmium, aluminum and magnesium metals.

A large number of the airports throughout the United States and other parts of the world experience snow and ice on the runways which must be cleared before normal operations may be resumed. The severity and frequency varies with respect to the geographical location. Although snow can be removed from the runways adequately by existing equipment, there is no satisfactory mechanical manner or removing ice or counteracting its low traction. lce on runways is considered to be particularly troublesome when it occurs in patches. The most promising method of combating the problem is to melt the ice with chemicals. The more common ice melting chemicals are calcium chloride and sodium chloride. These have been extensively employed to melt ice on roads, but they are too corrosive to be used on aircraft runways. The use of urea has been approved on the basis of no harm to aircraft by several major airlines. Other airlines have used urea with mixed results, primarily because of its limited effectiveness due to its relatively high eutectic point.

A deicer solution containing primarily formamide with other materials such as acetamide and urea is disclosed in U.S. Pat. No. 3,108,075. This fluid is stated to have negligible corrosion to aluminum and copper; however, no reference is made to corrosion of cadmium or magnesium used in fabricating aircraft surfaces. Moreover, formamide is relatively expensive and has limited availability.

U.S. Pat. No. 3,185,648 relates to a solid deicer composition consisting or urea and ammonium nitrate and a corrosion inhibitor. Several corrosion inhibitors are suggested; however, we have found that none of the disclosed corrosion inhibitors are effective to eliminate corrosion of cadmium, which is used for plating aircraft surfaces, particularly landing gear.

While U.S. Pat. Nos. 3,185,648 and 3,108,075 have contributed to the art, research in this field has continued in an effort to find still better deicing compositions and better corrosion inhibitors.

SUMMARY OF THE INVENTION An object of this invention is to provide an effective deicer solution containing a corrosion inhibitor for protection of cadmium, aluminum and magnesium metals with which the solution is contacted.

Another object of the present invention is to provide a liquid urea-ammonium nitrate-ethylene glycol deicer composition which is stable during storage at temperatures as low as l F. and which contains a novel inhibitor for controlling corrosiveness to cadmium.

[t has been found that these and other objects are obtained by formulating an aqueous deicer composition containing about 22 to 26 percent by weight of urea, about 28 to 34 percent by weight of ammonium nitrate, about 25 to 30 percent by weight of ethylene glycol, about 0.05 to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.04 percent by weight of a water-soluble chromate salt. The chromate and mercaptobenzothiazole salts are efiective to inhibit corrosiveness of the deicer solution toward cadmium, magnesium and aluminum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT This invention relates to a composition having a low freezing point which is particularly applicable to the deicing of aircraft runways.

The composition of the present invention is an aqueous chloride-free fluid deicer composition which has a marked depressing action on the melting point of ice and which is essentially harmless to metal surfaces it may contact, including cadmium, aluminum, magnesium, and their alloys. Moreover, the deicer composition of our invention is more effective as an ice melter on a weight basis than urea.

The preferred deicer solution contains about 22 to 23 percent by weight urea, about 29 to 30 percent by weight ammonium nitrate, about 24 to 25 percent by weight ethylene glycol, about 0.05 to 0.02 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.20 percent by weight of a water-soluble chromate salt, the balance of the solution substantially consisting of water. These low levels of inhibitor concentration have been found to inhibit corrosion of magnesium, aluminum and cadmium metals, including cadmium plated metal surfaces. Especially preferred water-soluble chromate salts and water-soluble salts of mercaptobenzothiazole include the readily available ammonium, sodium and potassium salts.

An especially preferred deicer solution is formulated as described above but about 0.05 to 0.50 percent by weight of an ammoniated superphosphoric acid is incorporated as corrosion inhibitor in addition to the chromate and mercaptobentothiazole inhibitors. An aqueous ammoniated superphosphoric acid is readily obtained by evaporating wetprocess phosphoric acid to form superphosphoric acid, which is then diluted with water and ammoniated to pH 5-8.

An aqueous ammoniated superphosphoric acid derived from wet-process phosphoric acid and having the following properties which will hereinafter be referred to as Solution A, has been found to be useful for purposes of the present invention;

Nitrogen IOk by weight Phosphorus (as P,O,) 34% by weight Trace minerals l to 2% by weight iron (Fe.,0 ca. 1.0% by weight calcium (CaO) ca. 0. I; by weight magnesium (MgO) ca. 0.3% by weight Specific Gravity at 60 F. l.4

Salting out temperature 0' F.

Distribution as L by weight of the ammonium phosphates present was about:

37% ammonium orthophosphate 49% ammonium pyrophosphate 8% ammonium tripolyphosphate 5% tetrapolyphosphate lk higher ammonium phosphates The preferred deicer composition of this invention can be stored at temperatures as low as about 104 F. without solidification of any of its components. Upon spraying the deicer solution on an iced runway, the eutectic temperature of the resulting mixture is about +l6.6 F. As compared with solid deicers such as urea, the deicer solution of the present invention is particularly desirable due to ease in handling. By means of spray nozzles on a moving vehicle, the desired coverage of any area can be accurately controlled.

The instant invention is particularly useful in conjunction with melting ice and snow on airport runways, taxiways, bus and truck loading areas where most of the equipment is constructed of several metals, including cadmium, aluminum and magnesium. However, if desired, utility of the invention may also be with the melting of ice and snow on roadways, sidewalks and the like.

The composition embodied herein may be prepared in any convenient manner providing a solution of the essential components. For example, urea and ammonium nitrate may be dissolved in water, either separately or combined, and then mixed in the proper proportions with ethylene glycol and inhibitors. In any event, the method whereby the noninhibited deicing composition embodied herein is prepared is not critical and is outside the scope of this invention. Any method which produces an aqueous solution of urea, ammonium nitrate, and ethylene glycol may be used.

The following examples are provided to more fully illustrate the instant invention. They are provided for illustrative purposes only and are not to be construed as limiting the invention, which is defined by the appended claims. In the following examples, all parts and percentages are by weight unless otherwise indicated.

EXAMPLE I A preferred deicer solution was prepared as follows: About 29.6 parts of ammonium nitrate and 22.8 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at a temperature of 77 F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution, followed by 0.2 parts of sodium chromate, tetrahydrate, and the mixture was stirred until the sodium chromate dissolved. Finally, 0.2 part of sodium mercaptobenzothiazole as a 50 percent aqueous solution was stirred into the mixture. The resulting solution was stored at temperatures as low as l0.4 F. without salting out. The deicer was used effectively to melt ice at temperatures of from l l F. to 32 F. However, the eutectic point was about l6.6 F.

EXAMPLE ll Chief problem encountered in developing a suitable deicer solution was corrosion of cadmium, magnesium and aluminum metal surfaces, which are used in aircraft. The deicer solution of example 1 was tested for corrosion of magnesium, cadmium and aluminum as follows:

A. Corrosion of Magnesium Magnesium panels were cleaned, rinsed with acetone, dried and weighed. The panels were then immersed in the deicer solution of example I for 7 days at room temperature. After the panels had been recleaned and reweighed, they were found to have a weight loss of about 2 milligrams per square inch. Five milligrams per square inch is the maximum allowable weight loss. A similar test with the deicer solution diluted with an equal part of water showed a weight loss of about I milligram per square inch.

in a comparative test, a deicer solution prepared as in example l but without corrosion inhibitors was tested in a similar manner with magnesium panels. Corrosion of the magnesium after a 7 day immersion was about 170 milligrams per square inch.

B. Corrosion of Cadmium A cadmium plated steel sample and a bead of cadmium metal were immersed for 3 days at room temperature in deicer solution prepared as in example l. No cadmium deterioration or removal of cadmium plating was observed. Similar results were obtained with the deicer solution diluted with an equal part of water.

In a comparative test, a deicer solution prepared as in example l but without sodium mercaptobenzothiazole was tested in a similar manner with a cadmium plated steel sample and a bead of cadmium metal. Deterioration of the cadmium metal was visible in one minute and removal of the cadmium plating appeared complete in 5 minutes.

C. Corrosion of Aluminum Thirty-six panels of six different aluminum alloys commonly used in aircraft construction were divided into three groups of six pairs of panels representing each alloy. Two groups of run panels were used to test diluted and undiluted deicer composition and the third group with water was used as control. Tap water, a 20 percent deicer solution, and a percent deicer solution, prepared in example I. were tested. The solution was applied to one side of each panel and two similar panels were placed together in sandwich style with the deicer solution between the two panels. The three groups of panels were exposed in a horizontal position at alternate intervals of 16 hours in a humidity chamber and 8 hours in an oven for a total of 7 days. The humidity chamber was maintained at 100 F. and 98 to l00 percent relative humidity. The oven was maintained at 100 F. After exposure, the panels were rinsed in warm tap water and scrubbed lightly with a soft brush. After drying the panels were examined under 15X magnification and each panel was rated according to the following standard:

0-No visible corrosion lVery slight corrosion or discoloration 2-Slight corrosion 3Moderate corrosion 4Extensive corrosion Results of the standard corrosion test are listed below:

Protection of high-strength aircraft landing gear from corrosion, including stress corrosion cracking, in the presence of deicer solutions is difficult due to the sensitivity of commonly used alloys both to stress corrosion cracking and embrittlement by hydrogen. This situation is complicated by the propensity of metal platings such as cadmium to introduce hydrogen during service.

Aircraft landing gear components consist primarily of A15] Type 4340 steel heat treated to an ultimate strength as high as about 280,000 p.s.i. Type 4340 steel is also used in the 220,000 to 240,000 p.s.i. range.

The deicer solution of example i was tested by a standard hydrogen embrittlement procedure using the Lawrence Hydrogen Detection Gauge and was rated Safe" in as far as hydrogen embrittlement is concerned for use on aircraft landing gear steel having a tensile strength of 200,000 p.s.i. or better. The deicer solution did not attack cadmium plate on the steel. These procedures satisfy the requirement of Douglas Bulletin 13-].

EXAMPLE IV Deicing Tests in Field A solution applicator for applying the deicer solution of example consisted of a l000-gallon stainless steel tank mounted on a tandem trailer. The rig was equipped with a 27- foot boom containing nine flood type nozzles on 2l0 -inch centers to give a 30-foot swath. Solution was sprayed through the nozzles by a positive displacement type pump driven by a ground wheel drive.

A taxiway covered with a sheet of ice one-sixteenth to oneeighth inch thick was treated with the deicer solution at rates of [5.5, 9.3. and 3.] pounds per 100 square feet. An area treated at the highest rate had water standing on it 30 minutes after treatment. The air temperature during this test was 23F. The next day all of the treated areas showed the effect of the deicer. The area treated with 15.5 pounds per 100 square feet was l00 percent bare and the other areas were 60m 80 percent bare. it is also noteworthy that the treated areas did not ice up during the next icing condition, indicating a residual effect of the deicer.

EXAMPLE V An especially preferred deicer solution was prepared as follows: About 29.4 parts of ammonium nitrate and 22.7 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at about 75F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution followed by 0.1 part of potassium mercaptobenzothiazole and 0.2 part of potassium chromate, and the mixture was stirred until the solids dissolved. Finally, 0.2 part of Solution A" was stirrred into the mixture. Solution A is an aqueous ammoniated superphosphoric acid containing polyphosphates, as described in detail hereinabove. The resulting deicer solution was similar to the solution of example I with respect to its salting out temperature and deicing properties. It passed all corrosion tests, previously described, for the product of example I including the standard hydrogen embrittlement test. Moreover, the combination of Solution A and sodium mercaptobenzothiazole was a particularly effective inhibitor against corrosion of cadmium plated steel. It appears that the polyphosphate in this solution provides a synergistic effect with respect to corrosion inhibition toward cadmium because solution A alone was found only slightly efiective in mitigating cadmium deterioration.

We claim:

I. A process for controlling corrosiveness to cadmium, aluminum, and magnesium metals of an aqueous deicer solution, said solution having a urea content of from about 22 percent to 26 by weight, an ammonium nitrate content of from about 28 percent to 34 percent by weight, and an ethylene glycol content of from about percent to percent by weight, which process comprises incorporating in said solution about 0.05 percent to 0.04 percent by weight of a water-soluble mercaptobenzothizaole salt and about 0.05 to 0.04 percent of a water-soluble chromate salt, based on the total weight of the solution.

3. A process as claimed in claim 1, further comprising incorporating in the deicer solution about 0.05 percent to 0.05 percent by weight of ammoniated superphosphoric acid.

3. A process as claimed in claim 1, wherein the mercaptobenzothiazole salt is selected from the group consisting of sodium mercaptobenzothiazole, potassium mercaptobenzothiazole and ammonium mercaptobenzothiazole, and about 0.05 percent to 0.20 percent by weight of the mercaptobcnzothiazole salt is incorporated based on the total weight of the solution.

4. A process as claimed in claim 1, wherein the chromatesalt is selected from the group consisting of sodium chromate, potassium chromate and ammonium chromate and about 0.05 percent to 0.20 percent by weight of the chromate salt is incorporated based on the total weight of the solution.

5. A process for controlling corrosiveness to cadmium, aluminum, and magnesium metals of an aqueous deicer solution, said solution having a urea content of from about 22 percent to 23 percent by weight, an ammonium nitrate content of from about 29 percent to 30 percent by weight, and an ethylene glycol content of from about 24 to 25 percent by weight, which process comprises incorporating in said solution about 0.05 percent to 0.20 percent by weight of sodium mercaptobenzothiazole and about 0.05 percent to 0.20 percent by weight of sodium chromate, based on the total weight of the solution.

6. As a new composition of matter of low corrosiveness toward cadmium, aluminum, and magnesium metals, an aqueous deicer solution containing from about 22 percent to 26 percent by weight urea, from about 28 percent to 34 percent by weight ammonium nitrate, from about 25 percent to 30 percent by weight ethylene glycol, from about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt, from about 0.05 percent to 0.04 percent by weight of a water-soluble chromate salt, and the balance substantially consisting of water.

7. A composition as claimed in claim 6, wherein the composition funher contains about 0.05 percent to 0.50 percent by weight of ammoniated superphosphoric acid.

8. A composition as claimed in claim 6, wherein the mercaptobenzothiazole salt is selected from the group consisting of sodium mercaptobenzothiazole, potassium mercaptobenzothiazole and ammonium mercaptobenzothiazole, and about 0.05 percent to 0.20 percent by weight of the mercaptobenzothiazole salt is present based on the total weight of the composition.

9. A composition as claimed in claim 6, wherein the chromatesalt is selected from the group consisting of sodium chromate, potassium chromate and ammonium chromate, and about 0.05 percent to 0.20 percent by weight of the chromate salt is present based on the total weight of the composition.

10. As a new composition of matter of low corrosiveness toward cadmium, aluminum, and magnesium metals, an aqueous deicer solution containing from about 22 percent to 30 percent by weight urea, from about 29 percent to 30 percent by weight ammonium nitrate, from about 24 percent to 25 percent by weight ethylene glycol, from about 0.05 percent to 0.20 percent by weight of sodium mercaptobenzothiazole, from about 0.05 percent to 0.20 percent by weight of sodium chromate, and the balance substantially consisting of water.

1* l i i II 33 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION pate N 3'624'243 Dated November 30, 1971 Inventgr(s) HERBERT F- SCOTT, JR. and WILLIAM P. MOORE It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- IN THE SPECIFICATION 1 Column 1, line 19, "geographical" should be geographic Column 1, line 72, "O. 04" should be 0. 40

Column 2, line l7, "0.02" should be 0.20

Column 2, line 62, "+l6.6F." should be -l6.6F. Column 4, line 20, "4Extensive" should be 4 Extensive Column 4, line 68, "210 inch" should be 40 inch Column 5, line 4, "60to" should be 60 to IN THE CLAIMS Column 5, claim 1, line 36, "26 by" should be 26 percent Column 5, claim 1, line 40, "0.04" should be 0.40 Column 5, claim 1, line 41, "0.04" should be 0.40 Column 5, claim 2, line 44, "3" should be 2 Column 5, claim 2, line 45, the second "0.05" should be Column 6, claim 5, line 12, "about 24 to" should be L about 24 percent to J 32 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, Dated November Inventor) HERBERT F. SCOTT, JR. and WILLIAM P. MOORE It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, claim 6, line 25, "0.04" should be 0.40

Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLEI'CHER,JR. ROBERT GOTTSCHALK Attesting Officer Co missioner of Patents 

3. A process as claimed in claim 1, further comprising incorporating in the deicer solution about 0.05 percent to 0.50 percent by weight of ammoniated superphosphoric acid.
 3. A process as claimed in claim 1, wherein the mercaptobenzothiazole salt is selected from the group consisting of sodium mercaptobenzothiazole, potassium mercaptobenzothiazole and ammonium mercaptobenzothiazole, and about 0.05 percent to 0.20 percent by weight of the mercaptobenzothiazole salt is incorporated based on the total weight of the solution.
 4. A process as claimed in claim 1, wherein the chromate salt is selected from the group consisting of sodium chromate, potassium chromate and ammonium chromate and about 0.05 percent to 0.20 percent by weight of the chromate salt is incorporated based on the total weight of the solution.
 5. A process for controlling corrosiveness to cadmium, aluminum, and magnesium metals of an aqueous deicer solution, said solution having a urea content of from about 22 percent to 23 percent by weight, an ammonium nitrate content of from about 29 percent to 30 percent by weight, and an ethylene glycol content of from about 24 to 25 percent by weight, which process comprises incorporating in said solution about 0.05 percent to 0.20 percent by weight of sodium mercaptobenzothiazole and about 0.05 percent to 0.20 percent by weight of sodium chromate, based on the total weight of the solution.
 6. As a new composition of matter of low corrosiveness toward cadmium, aluminum, and magnesium metals, an aqueous deicer solution containing from about 22 percent to 26 percent by weight urea, from about 28 percent to 34 percent by weight ammonium nitrate, from about 25 percent to 30 percent by weight ethylene glycol, from about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt, from about 0.05 percent to 0.40 percent by weight of a water-soluble chromate salt, and the balance substantially consisting of water.
 7. A composition as claimed in claim 6, wherein the composition further contains about 0.05 percent to 0.50 percent by weight of ammoniated superphosphoric acid.
 8. A composition as claimed in claim 6, wherein the mercaptobenzothiazole salt is selected from the group consisting of sodium mercaptobenzothiazole, potassium mercaptobenzothiazole and ammonium mercaptobenzothiazole, and about 0.05 percent to 0.20 percent by weight of the mercaptobenzothiazole salt is present based on the total weight of the composition.
 9. A composition as claimed in claim 6, wherein the chromate salt is selected from the group consisting of sodium chromate, potassium chromate and ammonium chromate, and about 0.05 percent to 0.20 percent by weight of the chromate salt is present based on the total weight of the composition.
 10. As a new composition of matter of low corrosiveness toward cadmium, aluminum, and magnesium metals, an aqueous deicer solution containing from about 22 percent to 23 percent by weight urea, from about 29 percent to 30 percent by weight ammonium nitrate, from about 24 percent to 25 percent by weight ethylene glycol, from about 0.05 percent to 0.20 percent by weight of sodium mercaptobenzothiazole, from about 0.05 percent to 0.20 percent by weight of sodium chromate, and the balance substantially consisting of water. 